1. Field of the Invention
The present invention relates to an electrically-heated wax spatula apparatus for use in molding and preparing wax models for investment casting in the field of dental prostheses and the field of metal work based on investment casting, and more particularly to a wax spatula apparatus wherein the temperature of its spatula portion for wax-molding work can be adjusted immediately during use.
2. Prior Art
A dental wax spatula apparatus is a wax-molding device for forming or preparing wax models for dental plates, crowns, etc. in a process wherein these dental parts are molded simultaneously from dental alloy materials by an investment casting technique, such as the lost-wax process. The wax spatula apparatus is also used frequently to shape wax models for metal work products made by the centrifugal casting process. Conventional wax spatula apparatuses are classified into a type that is used while being heated by a burner and another type in which the apparatuses are provided with a heater so as to generate heat by itself.
A process of molding a wax model by using a wax spatula apparatus includes an operation step wherein the heated spatula portion of the spatula apparatus is put into wax (material) in order to melt the wax, a certain amount of the wax is cut off, and the wax is piled up on a predetermined base. Furthermore, the process includes another operation step wherein the wax piled up on the base is softened and molded into a desired shape by partially shaving and moving the wax or by adding a further amount of the wax. Moreover, the process includes still another operation step wherein the surface of the molded wax is smoothened or provided with fine patterns. The spatula portion is required to heated at an optimum temperature at each of the operation steps. It is therefore necessary to quickly change and finely adjust the temperature of the wax in the range of the melting temperature to softening temperature of the wax.
Although conventional electrically-heated wax spatula apparatuses are publicly known, they are not necessarily satisfactory in temperature control. In addition, the spatula portion of such a wax spatula apparatus is required to be replaced with another spatula portion having a shape suited for each of the above-mentioned operation steps. The replacement of the spatula portions makes it difficult to quickly redo temperature control.
There has been known a type of spatula apparatus having an electrically resistant gap, made of metal and being somewhat electrically conductive, formed to divide its spatula portion into two half tips in its width direction, wherein the gap between the tips of the two halves is short-circuited with a heating resistor, and electric power is applied to the halves to heat the resistor (see Japanese Patent Publication No. 7-15006, for example). Although this type of spatula apparatus has an advantage of quick thermal response since the heating portion is short-circuited through the gap at the tip of the spatula portion, it has a difficulty in accurately detecting the temperature of the tip. In other words, current or power supply time has to be adjusted manually, then roughly controlling the temperature of the spatula portion to an temperature required each time the spatula portion is used for wax-molding work.
A modified electrically-heated spatula apparatus invented by the applicants of the present invention has been disclosed in Japanese Patent Publication 10-108872. This spatula apparatus is provided with a heating portion having a ceramic tube with a small electric heating element and a small temperature sensor inserted therein, which heating portion is secured to the tip of the grip portion of the spatula apparatus. Some spatula portions which are formed of a metal spatula in the shapes of plate, knife, spear, needle, and the like, can be exchangeably attached to the heating portion at the tip of the grip portion. Furthermore, the spatula portion can be heated to a desired temperature by thermal conduction from the electric heating element capable of being controlled at two or more levels of preset temperature. This thermally controlled spatula portion have favorably been used to heat and mold wax material.
This spatula apparatus is provided with a temperature controller that controls electric power supplied to the electric heating element while measuring the actual temperature of the spatula portion by using the temperature sensor so that the temperature at the spatula portion can be set at least at two or more levels. The spatula apparatus is also provided with independent temperature selection means for setting temperatures, such as a footswitch or hand switch.
This conventional apparatus has an advantage of being capable of facilitating wax-molding work by setting temperatures at multiple levels by using the temperature selection means. Since the temperature selection means can set two or more temperature levels, the apparatus has an advantage of adjusting the temperature of the spatula portion to a value best suited for each step of spatula operations as described above. In a course of wax work, for example, first, the temperature of the spatula portion is set at a value higher than the melting temperature of wax, and this temperature is used for scooping up a small amount of wax from a wax lump sequentially with said spatula portion and placing it on an object wax model. Then, the temperature of the spatula portion is set at another value lower than the wax melting temperature but higher than the wax softening temperature, and this temperature is used for precisely sculpturing the surfaces of the wax model.
However, in the case of the conventional spatula apparatus, a footswitch or a hand switch have been used to set the temperature of the spatula portion. Although the footswitch or the hand switch can be operated at each change of the preset temperature of the spatula portion during the wax-molding work, the temperature cannot be changed as promptly as is expected, or wax-molding work is not necessarily carried out efficiently; therefore, the operability of the apparatus is unsatisfactory. In addition, since other apparatuses than the spatula apparatus have also been operated frequently by using footswitches in the working environments of dental technicians, the apparatuses may be involved in a danger of being operated improperly.
Furthermore, the so-called cone technique is used to make wax models for artificial teeth. This is an advanced and delicate technique wherein a melted wax lump is solidified and raised like a hone while being cooled by blowing breaths on it delicately when a front tooth or the cusp portion of a molar tooth is molded. A conventional burner-type spatula is suited for this operation since the spatula is cooled spontaneously at an appropriate cooling speed during use. However, in the case of the electrically-heated spatula, its temperature is required to be lowered intentionally. For this purpose, the operator has no choice but to turn off supply power to the electric heating element of the spatula by manually operating the control panel or the above-mentioned footswitch by moving the operator""s hand or foot during wax-molding work. This operation is troublesome for the operator since the operator is conducting delicate wax-molding work with both hands.
Accordingly, an object of the present invention is to provide a wax spatula apparatus capable of carrying out delicate temperature adjustment at a spatula portion required for wax-molding work and also capable of lowering and raising the temperature of the spatula portion quickly and accurately by simple human operation.
Another object of the present invention is to accomplish the setting of the temperature of the spatula portion and the controlling of electric power supplied to the electric heating element of the spatula portion required for the setting by using only a fingertip of the hand gripping the spatula, thereby to eliminate the above-mentioned troublesome hand or foot operation.
In the present invention, a temperature-setting switch of temperature-setting means is disposed on a grip portion of the spatula body, and the temperature of the spatula portion is raised or lowered to any of preset values of temperature by operating the above-mentioned switch with a fingertip.
The spatula apparatus in accordance with the present invention comprises a spatula body, which is provided with a heating portion accommodating an electric heating element and a temperature sensor at the front end of the grip portion thereof and a wax-molding spatula portion installed in the heating portion, and a temperature controller for controlling the temperature of the spatula portion by supplying electric power to the electric heating element of the heating portion and by controlling the electric power depending on a temperature signal from the temperature sensor of the heating portion. The temperature controller comprises preset temperature selection means capable of independently selecting a plurality of temperature levels and temperature-setting means capable of setting the temperature of the spatula portion at a selected temperature level. The temperature-setting means includes the temperature-setting switch. By operating the switch, the preset temperature of the spatula portion is raised or lowered to a new, desired temperature value. The temperature controller quickly adjusts the temperature of the spatula portion to the newly preset temperature value by heating or cooling the spatula portion.
In the present invention, the temperature-setting switch is secured to the grip portion of the spatula body so as to be operable with a fingertip. With this configuration, the temperature of the spatula portion can be changed and adjusted by operating the switch easily and quickly during wax-molding work.
The preset temperature selection means is intended to select one of two, three or more temperature levels. The selection switch of the preset temperature selection means is preferably installed in the temperature controller. With this configuration, the selection switch is used to select preset temperature levels so that the temperature of the spatula portion can be switched from a temperature level to another temperature level immediately. Furthermore, the setting of the preset temperature of the spatula portion at the temperature level selected by the temperature-setting switch secured to the grip portion is changed to adjust the temperature of the spatula portion. As a result, the operator can adjust the temperature of the spatula portion in a required range by performing only switch selection. The efficiency of work can thus be improved.